The present invention is directed to the use of Delta-like protein (dlk) to inhibit the rate of differentiation of stem cells.
The differentiated cells of some biological systems mature in stages from a common progenitor cell, usually called a stem cell. Such cells include, for example, hematopoietic, neural, epithelial, endothelial, and mesodermal cells.
Stem cells are able to differentiate into mature cells within one of these systems. Differentiation may occur through uncommitted or committed progenitor cell intermediates.
The differentiation of a stem cell may result in one mature cell. Alternatively, a stem cell may differentiate into multiple mature lineages within a biological system, in which case the stem cell is said to be pluripotent. In some cases, the differentiation of a stem cell may result in all the mature lineages of an entire biological system, in which case the stem cell is said to be totipotent. Stem cells are also be able to self-renew. The self-renewal must be delicately balanced by differentiation in order to maintain a healthy level of stem cells.
For example, hematopoietic stem cells constitute approximately 0.01% of the cells in adult bone marrow. These stem cells, which can be recognized by the presence of the CD34 antigen, are found in micro-environments associated with stromal cells.
Hematopoietic stem cells are induced by various cytokines, such as c-kit and flk-2/flt-3 ligand, to differentiate into increasingly lineage-committed progenitors. These progenitors differentiate further into the various mature white blood cells, red blood cells, and platelets of the hematopoietic system.
Self-renewal of the stem cells requires their maintenance in an undifferentiated state. There are various applications for methods that increase the time during which stem cell populations remain undifferentiated in vivo and ex vivo. Such applications include, for example, gene therapy, and concentrating stem cell populations.
Another application for maintaining stem cells in an undifferentiated state is cell and tissue transplantation between animals. An example of this application, in the case of hematopoietic cells, is bone marrow transplantation.
Attempts to maintain and expand stem cells, especially hematopoietic stem cells, using various cytokines and cytokine mixtures have been unsuccessful. An object of the present invention is to provide methods for the maintenance of stem cells in an undifferentiated state. A more specific object is to provide methods for the maintenance of hematopoietic stem cells in an undifferentiated state. Another object is to provide a method for enriching a population of stem cells in a mixture of stem cells and non-stem cells.
These, and other, objects as will be apparent to those having ordinary skill in the art have been met by providing a method for inhibiting the differentiation of stem cells, such as hematopoietic stem cells; and a method for enriching a population of stem cells in a mixture of stem cells and non-stem cells. The methods comprise contacting the stem cells, or the mixture of stem cells and non-stem cells, with a sufficient amount of human delta-like protein (dlk).